1. Field of the Invention
The present invention relates generally to a clutch apparatus for allowing rotation of a first race member in a first direction relative to a second race member, while preventing rotation of the first race member in a second direction relative to the second race member and, more specifically, to an overrunning clutch apparatus for maintaining lubricant in contact with a unidirectional drive means located between the first race member and the second race member.
2. Description of the Prior Art
Overrunning clutches typically have an interior race keyed to a shaft or other drive mechanism and an exterior race concentrically located around the inner race with an annular space therebetween. Provided within the annular space is a unidirectional drive means which transmits torque between the races when one of the races is rotated in a first direction relative to the other, but which does not transmit torque when the race is rotated in the opposite direction.
One type of overrunning clutch, a sprag clutch, has a unidirectional drive means comprising a plurality of asymmetrical tumblers or sprags provided within a retainer. When one race is rotated in a first direction relative to the other, the sprags are biased into an upright position by springs or similar resilient means. Because the sprags are too large to move fully upright, they jam or wedge between the races, thereby transmitting torque between the races. When the race is rotated in the opposite direction, the sprags are tilted sideways into an overrunning position, so that no torque is transmitted between the races.
Even when the sprags are in their overrunning position, the spring still biases the tips of the sprags into contact with both races. Although little or no torque is transmitted between the races when the sprags are in the overrunning position, the high speeds of the races relative to the sprags causes a constant wearing between the sprags and the races. Without adequate lubrication, this wearing between the sprags and races would quickly deteriorate the sprags. Constant lubrication is therefor imperative.
Many prior art designs have been suggested for maintaining lubrication on the sprags to alleviate premature wear when the clutch is in the overrunning position. U.S. Pat. No. 4,875,564 Leitz, et al. discloses one embodiment of a sprag assembly which includes an outer sprag cage ring, an inner sprag cage ring, and a pair of lateral disks enclosing the sprags and preventing undesirable lateral displacement of the sprags. The lateral disks may be provided with bores which allow the introduction of oil into contact with the sprags to reduce wear and friction.
In this invention, however, the placement of the inner sprag cage ring prevents the lateral introduction of a lubricant near the innermost portions of the sprags. Any lubricant induction bores must be generally centered between the outer and inner circumferences of the lateral disks. This centering of the bores, combined with the centrifugal force of the rotating clutch, prevents the innermost portions of the sprags from being fully lubricated. The centering of the bores also allows a lubricant to escape from the sprags back through the bores. Additional escape of lubricant is provided by holes used to connect the outer sprag cage ring to the lateral disks.
It would therefor be desirable to eliminate the outer cage ring connection holes and to provide a bore closer to the inner race. In this way, lubricant could be supplied to the innermost portions of the sprags, while reducing escape of the lubricant through the bores. Additionally, it would be desirable to provide means for retaining excess lubricant within the space between the inner race and outer race, even if the lubricant were to become inadvertently expelled from the sprag retainer.
The difficulties encountered in the prior art discussed hereinabove are substantially eliminated by the present invention.